1. Field of the Invention
The present invention relates to a driving device for driving a recording head provided with plural heat generating elements by dividing the head into plural blocks each having plural heat generating elements, and a recording apparatus provided with the driving device.
2. Related Background Art
In a thermal printer equipped with a line type thermal head, the printing characteristics are often influenced by the temperature of the thermal head. For this reason, the heat generating elements of the thermal head are driven in plural blocks, in order to prevent a rapid temperature increase of the entire thermal head, thereby avoiding rapid fluctuation in printing characteristics. This type of divided drive offers the advantage of reducing the capacity of the power source needed for driving the thermal head, as the electric power used in driving the thermal head can be reduced.
FIG. 28 shows the timing of conventional pulse application in solid black printing, in which a first pulse activates the heat generating elements of a divided block driver 201, and a second pulse activates those of another driver 202.
However, such divided drive results in portions of lower print density, so-called division lines, at the boundaries of the recording blocks. This is because the heat generating elements (R.sub.k, R.sub.k+1) at the boundary of the blocks are lower in temperature, as they are always at the end of energized blocks and are subjected to heat dissipation from the ends, thus resulting in a lower recording density.
For avoiding the formation of such division lines, various methods have been proposed, such as a method of applying a correcting coefficient to the recording data at the ends of each divided block as disclosed in the Japanese Patent Application Laid-open No. 60-132771, or a method of using an element at the boundary of two divided blocks in common for the blocks, as disclosed in the Japanese Patent Application Laid-open No. 61-29272. However, even with these methods, division lines are formed at the boundaries of the blocks of the recorded image, detracting from the quality of the image, depending on the ambient temperature or the increase or decrease of the temperature, or depending on the tonal rendition of the image.